There are known electronic devices including a LCD touch screen used to activate the various functions of the device.
For example, there are known watches including a so-called touch glass having, on the lower face thereof, capacitive electrodes acting as touch keys. These keys are activated by a conventional push-piece. This activation of the touch keys consists in scanning them. This means that each key is monitored at a certain frequency to see whether there is a depression, i.e. a capacitance variation. A high scanning frequency on the order of 64 Hz is used to detect the different depressions and different touch operations. The user then touches the location of a capacitive electrode to activate the desired function.
One drawback of this method is that the user must pre-activate the touch keys before selecting a function and this therefore requires an additional operation. Further, this configuration requires a key to activate a function, which consequently limits the number of functions that the device can have.
There are also known electronic devices provided with a touch screen. This touch screen is permanently activated so that, at any time, the user can operate the electronic touch device. This means that all of the touch keys are scanned at a high frequency. Although this is convenient for the user during operations, this configuration also has the drawback of being energy intensive. Indeed, this permanent scanning requires continuous use of the microprocessor or microcontroller which controls the touch display. This results in high electrical power consumption.